In all animals, the germ cells (precursors to eggs and sperm) form very early in development. The region of the embryo at the posterior pole destined to make germ cells contains special structures called polar granules in Drosophila. This proposal is aimed toward using Drosophila to increase our understanding the mechanism of germ cell formation and development. The major focus will continue to be on Vasa (Vas), a protein which is localized in polar granules and essential for the development of germ cells in Drosophila. Previous work supports the hypothesis that Vas activates translation of specific mRNAs essential for germline development through an association with dIF2, which is identical to the general translation initiation factor elF5B. Experiments are planned to test this hypothesis and to understand the mechanism by which Vas and elF5B regulate translation of specific germ line mRNAs. Many proteins and RNAs involved in oocyte development and patterning accumulate in ribonucleoprotein particles, which are likely to be involved in their correct deployment and in translational control. We identified a new protein component of these RNPs called Gustavus (Gus). In a gus mutant we isolated, Vas is not localized to the posterior of the oocyte; nor is a mutated form of Vas that lacks a short domain essential for Gus binding localized in wild-type oocytes. Thus gus is essential for Vas deployment. We are planning additional experiments to clarify the role of gus in pole plasm assembly. Furthermore, several molecular and genetic approaches will be pursued to derive a more complete understanding of the protein and ANA components of germline patterning RNPs. This work will provide important information on the formation and maturation of germ cells, which will ultimately provide a fundamental framework for understanding the basis of many problems leading to human infertility.